Method and system for the indication of long drx in a wireless network

ABSTRACT

Methods and apparatus for configuring a discontinuous reception ‘DRX’ period at from an evolved Node B for a user equipment, including: sending a long DRX MAC CE from the eNB if preconditions are met, and at the UE determining whether a short DRX period is configured; if no, setting a long DRX period; if yes, determining whether a long DRX command was received in a medium access control ‘MAC’ control element; if yes, setting the long DRX period; if no, starting a short DRX timer and setting a short DRX period.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority from U.S. ProvisionalApplication Ser. No. 61/038,432, filed Mar. 21, 2008, the contents ofwhich are incorporated herein by reference.

FIELD OF THE DISCLOSURE

The present disclosure relates to the long term evolution (E-UTRA) ofThird Generation Partnership Project (3GPP), and in particular todiscontinuous reception (DRX) for user equipment (UE) in the E-UTRAinfrastructure.

BACKGROUND

In the long term evolution infrastructure, a UE can be in one of tworadio resource control (RRC) states. These are LTE_IDLE and LTE_ACTIVE.

The UE can be configured for discontinuous reception (DRX) in both theLTE_IDLE and the LTE_ACTIVE states. DRX allows the UE to synchronize itslistening period to a known paging cycle of the network. Bysynchronizing the listening period, the UE can turn off its radiotransceiver during the standby, thereby significantly saving batteryresources. As will be appreciated by those skilled in the art, unless aUE is used extensively, a large drain on its battery comes from thestandby cycle in which it monitors the paging channel and measuresserving and neighboring cells. DRX parameters allow the mobile tosynchronize with the network and to know that it will not receiveanother signal until a specified time has elapsed.

Utilizing DRX in an IDLE state is performed in present UMTS systems andis done by the network signaling to the UE a DRX parameter andsynchronizing the UE and the network. As will be appreciated, in IDLEmode the UE can change cells from one cell to the other. Thus utilizinga DRX parameter does not cause significant issues.

In an ACTIVE state however, various issues exist for turning off thereceiver based on a DRX parameter. This includes the fact that onlynetwork controlled handover is allowed in the LTE_ACTIVE state. Also,other issues include efficient signaling of activation and deactivationof DRX, measurement requirements of network signals during the DRX,handling of missed handover opportunities, and issues dealing with thelength of the DRX value in which entity in the network can request DRXactivation and reconfiguring the DRX period.

In current systems, when short and long DRX is configured for non realtime traffic and the traffic volume becomes very low, the eNB wants toput the UE which may be either in short DRX or actively listening todownlink common control channels into long DRX, for further batterysaving if there is no uplink and downlink transmission. In currentE-UTRA specifications, the eNB needs to deactivate short DRX using a RRCreconfiguration message at first and then issue a go-to-sleep MACcontrol element (CE). If traffic pattern changes, however, the eNB needsto activate short DRX by RRC again.

BRIEF DESCRIPTION OF THE DRAWINGS

The present application will be better understood with reference to thedrawings, in which:

FIG. 1 is a block diagram showing a long term evolution user planeprotocol stack;

FIG. 2 is a block diagram showing a long term evolution control planeprotocol architecture;

FIG. 3 a is a flow chart showing a method to activate deactivate andreconfigure DRX period using a MAC-PDU header from the eNB side;

FIG. 3 b is a flow chart showing a method to acknowledge the activation,deactivation or reconfiguration of the DRX period from the UE side;

FIG. 4 a is a flow chart showing a method for a UE to leverageapplication traffic characteristics to improve battery life from the UEside;

FIG. 4 b is a flow chart showing a method for a UE to leverageapplication traffic characteristics to improve battery life from the eNBside;

FIG. 5 is a diagram showing signal strength thresholds and measurementcycle times;

FIG. 6 a is a flow chart illustrating procedural steps involved inswitching to a target eNB from the UE side;

FIG. 6 b is a flow chart illustrating procedural steps involved inswitching to a target eNB from the eNB side;

FIG. 7 is a graph showing channel status going below a lower thresholdvalue and then above a threshold value without any uplink data;

FIG. 8 is a graph showing channel status going below a lower thresholdvalue and then above a higher threshold value with uplink data;

FIG. 9 is a graph showing signal degradation in which a handovercondition is triggered;

FIG. 10 a is a flow chart showing a method to transition directly tolong DRX period using a MAC-PDU header from the eNB side; and

FIG. 10 b is a flow chart showing a method to transition directly to along DRX period from the UE side.

DETAILED DESCRIPTION OF THE DRAWINGS

The present disclosure provides various methods and systems foraddressing the deficiencies in the prior art regarding DRX in anLTE_ACTIVE state.

In particular, a DRX signaling procedure between the UE and the eNB, inwhich the eNB signals DRX values and timing margins as part of amodified MAC-PDU header, is described. The eNB signaled DRX value canrange from zero to indicate DRX deactivation to a value for the DRXperiod. The timing margin can indicate a delay for activating DRX toovercome NACK-ACK misinterpretations or ACK-NACK misinterpretations. Inone embodiment the timing margin can be also signaled by the RRC.

In a further embodiment, the DRX value can be a relative value that ispredefined on the eNB or the UE or a pre-configured value by RRCsignaling. Thus a “short DRX value” could be used to indicate a shortDRX period and a “long DRX value” could be used to indicate a long DRXperiod. In further embodiments, more than two values are possible. Inthis case, the eNB can signal, for example, a long DRX value in a“go-to-long-sleep” command to allow the UE to proceed directly to longDRX without having to transition first to a short DRX value and wait forthe short DRX period timer to expire before transitioning to a long DRXperiod, and without RRC reconfiguration commands.

The DRX value, in one embodiment can be incrementally increased to acertain maximum value that will be either defined in the standards orsignaled. The increment may be carried out without signaling by both theUE and the eNB if no data has been received for a preset number of DRXcycles. In a further embodiment, the DRX value can be incrementallydecremented until DRX is deactivated without signaling by both the UEand the eNB. In a further embodiment, application level trafficcharacteristics can be leveraged for an optimization of the DRX periodto improve battery life. The UE could, in this case, send a request toinitiate or amend a DRX value to the eNB and the eNB can either acceptthis value or reject it. Various considerations including mobility,location of the cell, traffic characteristics, or missed handoveropportunities can be determined for both the UE and the eNB in choosingand accepting a DRX value.

In a further embodiment, measurement accuracy may be improved byshortening the measurement cycle from the DRX cycle if a certainthreshold signal value is reached for a certain amount of time. Thus, inthe case of signal degradation, the UE may decide that more frequentmeasurement needs to be performed if the quality of the signal fallsbelow a threshold for a predetermined time. Subsequently, themeasurement cycle can be increased if the signal rises above a thresholdfor a certain time period, or a handover condition can be triggered ifthe signal falls below a threshold.

In a further embodiment, missed handover opportunities can be handled ifthe channel quality or signal strength of a serving cell is less than aneighboring cell by a threshold value for a certain duration. Proceduresfor switching to a target eNB are disclosed.

The present disclosure therefore provides a method of DRX signaling in along-term evolution infrastructure between an evolved node B (eNB) anduser equipment (UE), the method comprising the steps of: providing a DRXvalue or coded DRX value in a header of a medium access control protocoldata unit (MAC-PDU); and activating, deactivating or reconfiguring DRXbased on the provided DRX value.

The present disclosure further provides a method of leveragingapplication level traffic characteristics to improve battery life ofuser equipment (UE) communicating with an evolved Node B (eNB)comprising the steps of: requesting, from the UE, a discontinuousreception (DRX) based on application traffic characteristics of the UE;receiving the request from the UE at the eNB; and granting, negotiatingan alternative period or rejecting the request at the eNB.

The present disclosure further provides a method for improvedmeasurement accuracy during discontinuous reception (DRX) on userequipment (UE) comprising the steps of: checking whether a channelquality or signal strength of a serving cell is lower than a firstthreshold for a predetermined time period; and if yes, shortening themeasurement cycle to have a shorter measurement cycle than the DRXcycle.

The present disclosure still further provides a method of handlingmissed handover opportunities based on discontinuous reception (DRX) inuser equipment (UE) comprising the steps of: checking whether a channelquality or signal strength of a serving cell is less than the channelquality or signal strength of a neighboring cell by a threshold valuefor a certain time duration; and if yes, connecting to the neighboringcell.

The present disclosure further provides: an evolved node B (eNB)operating in a long-term evolution infrastructure, the eNB beingcharacterized by means for providing a DRX value in a header of a mediumaccess control protocol data unit (MAC-PDU); and activating ordeactivating DRX based on the DRX value.

The present disclosure still further provides a user equipment (UE)operating in a long-term evolution (LTE) infrastructure, the UE beingcharacterized by means for receiving a DRX value in a header of a mediumaccess control protocol data unit (MAC-PDU) and acknowledging theMAC-PDU; and activating, deactivating or reconfiguring DRX based on theDRX value.

Reference is now made to the drawings. FIG. 1 shows a block diagramillustrating the long-term evolution (LTE) user plane protocol stack.

A UE 110 communicates with both an evolved Node B (eNB) 120 and anaccess gateway (aGW) 130.

Various layers are illustrated in the protocol stack. The packet dataconvergence protocol (PDCP) layer 140 is illustrated both on the UE 110and on aGW 130. The PDCP layer 140 performs internet protocol (IP)header compression and decompression, encryption of user data, transferof user data and maintenance of sequence numbers (SN) for radio bearers.

Below the PDCP layer 140 is the radio link control protocol layer 142,which communicates with the radio link control protocol layer 142 on theeNB 120. As will be appreciated, communication occurs through thephysical layer in protocol stacks such as those illustrated in FIGS. 1and 2. However, RLC-PDUs from the RLC layer 142 of the UE areinterpreted by the RLC layer 142 on the eNB 120.

Below RLC layer 142 is the medium access control (MAC) datacommunication protocol layer 146. As will be appreciated by thoseskilled in the art, the RLC and MAC protocols form the data linksublayers of the LTE radio interface and reside on the eNB in LTE anduser equipment.

The layer 1 (L1) LTE (physical layer 148) is below the RLC/MAC layers142 and 146. This layer is the physical layer for communications.Referring to FIG. 2, FIG. 2 illustrates the LTE control plane protocolarchitecture. Similar reference numerals to those used in FIG. 1 will beused in FIG. 2. Specifically, UE 110 communicates with eNB 120 and aGW130. Further, physical layer 148, MAC layer 146, RLC layer 142 and PDCPlayer 140 exist within FIG. 2.

FIG. 2 also shows the non-access stratum (NAS) layer 210. As will beappreciated, NAS layer 210 could include mobility management and sessionmanagement.

The radio resource control protocol layer (RRC) 220, is the part of theprotocol stack that is responsible for the assignment, configuration andrelease of radio resources between the UE and the E-UTRAN (Evolveduniversal terrestrial radio access network). The basic functionalitiesof RRC protocol for LTE is described in 3GPP TR25.813. As will beappreciated by those skilled in the art, in UMTS, automatic repeatrequest (ARQ) functionality is carried out within the RLC layer whichresides in the radio network controller (RNC). Long Term Evolution (LTE)moves the ARQ functionality from the RNC to eNB where a tighterinteraction may exist between the ARQ and the HARQ (within the MAClayer, also located in the eNB).

Various issues regarding DRX in an LTE-ACTIVE state are consideredherein.

DRX Signaling Procedure

Very efficient signaling procedures for activating and de-activating DRXand specifying the duration of DRX periods are required in order tosupport a large population of UEs in a cell that are utilizing DRX in anLTE_ACTIVE state.

As will be appreciated by those skilled in the art, if the evolved nodeB (eNB) transmits data to the UE during its receiver off period due to aDRX operation, the UE cannot receive the data. Therefore, an indicationis required to ensure the UE and the eNB are synchronized regarding whenDRX is activated and deactivated.

The indication between the UE and the eNB can be explicit signaling bythe radio resource control (RRC) or layer 1/layer 2 (L1/L2) signaling.As will be appreciated, however, explicit signaling may not be asefficient as desired.

A more efficient solution is to include an optional field in the MACheader of a MAC-PDU (MAC Protocol Data Unit) to indicate DRX activationand deactivation. The field preferably indicates the DRX value andtiming margin for activation and deactivation. A value of zero, forexample, could mean DRX deactivation in the DRX value field in apreferred embodiment. Conversely, if data that is to be transmitted inthe next MAC-PDU is the last one in the buffer for the UE, the eNB mayextend the MAC header field to include a DRX length initial value. Forexample, this could be 320 milliseconds. The timing margin is explainedbelow, and is utilized to reduce the consequences of a NACK to ACK orACK to NACK misinterpretation, for the reception status of the MAC-PDUbetween the UE and the eNB. For example, three bits may be added to theMAC header to indicate eight values of the DRX period. Thus, rather thana specific time value being sent, a bit value from 000 to 111 couldindicate one of eight discrete values.

In an alternative, a smaller field in the MAC header could be used (forexample two bits) to indicate increment or decrement. The RRC couldindicate default values, and if the MAC header indicates increment ordecrement then the UE could change to the prespecified value.

Once the UE receives the DRX value, it acknowledges it to the eNB bytransmitting HARQ ACK and starts the DRX at the system frame timeconsidering propagation delay and processing delay at the eNB. When theeNB receives the ACK from the UE, it also starts the DRX at the nextsystem frame time. As will be appreciated, the eNB does not turn off itstransceiver, but simply knows not to transmit messages to the individualUE.

During a DRX period, if new data arrives at the eNB, the eNB can send aMAC-PDU with a header extension set to DRX deactivation or a shorter DRXlength depending on the amount of data in the buffer or the quality ofservice requirements. The UE reconfigures the DRX accordingly andacknowledges the MAC-PDU. When the eNB receives the ACK, it reconfiguresthe DRX. As indicated above, the deactivation could be accomplished bymerely setting the length value to zero.

Reference is now made to FIGS. 3 a and 3 b. FIG. 3 a shows an exemplarymethod for controlling DRX activation in an LTE_ACTIVE state. Theprocess starts at step 300 and proceeds to step 310 in which data istransmitted to the UE. As will be appreciated by those skilled in theart, data transmission in an LTE_ACTIVE state utilizes the MAC-PDU atthe data link layer to transmit the data.

The process next proceeds to step 312 in which a check is made to seewhether the buffer of data to be sent to the UE will be empty after thenext transmit. If no, the process proceeds back to step 310 in whichdata is transmitted to the UE. Alternatively, if the buffer will beempty after the next transmit and the data arrival rate is lower than athreshold value, the process proceeds to step 314.

In step 314, the eNB sets DRX activation in the MAC-PDU header. Asindicated above, this includes a DRX activation value indicating thelength of the DRX period. In another embodiment the eNB may simplyindicate an increase in the DRX interval. The UE reconfigures theexisting DRX interval to a predetermined reduced interval. Thepredetermined interval may be either known to both eNB and UE orpre-signaled to the UE from the eNB via explicit signaling; either bysystem broadcast or RRC signaling.

The process then proceeds to step 316 in which the data including themodified MAC-PDU header is sent to the UE.

Reference is now made to FIG. 3 b. In step 318, the UE receives the dataand sees that DRX activation is specified in the MAC-PDU header. Theprocess proceeds to step 320 in which the UE sends an acknowledgement(ACK) to the eNB and starts the DRX at the system frame time consideringpropagation delay and processing delay at the eNB.

In step 330 of FIG. 3 a, the eNB receives the ACK from the UE and startsthe DRX at the next system frame time.

As will be appreciated, the DRX can continue until various events occurwhich may require the DRX to be adjusted. One event is the reception ofdata from aGW by the eNB for the UE. Depending on the amount of datareceived, the DRX can either be deactivated or the period of the DRX canbe reduced. Other events that may require the adjustment of the DRXinclude a change of signal power level between the eNB and the UE orpossibly a gradual increase in the DRX cycle due to continued datainactivity, among others. These other events are discussed in moredetail below.

In step 332 the eNB checks to see whether the DRX needs to be adjusted.As indicated above, this could be the situation where data is receivedto be sent to the UE. Here the DRX can either be deactivated or theperiod adjusted.

From step 332, if the DRX does not need to be adjusted, the processproceeds back to step 332 and continues to check whether or not the DRXneeds to be adjusted.

Once the process in step 332 finds that the DRX does need to beadjusted, the process proceeds to step 334 in which it adjusts the DRX.This could be deactivating the DRX by transmitting a zero value for theDRX or a shorter DRX or a longer DRX as required.

The MAC-PDU with the modified header is sent to the UE in step 336. TheMAC-PDU in step 336 could also include any data that has been receivedby the eNB that needs to be transmitted to the UE.

Referring to FIG. 3 b, the process then proceeds to step 318 in whichthe MAC-PDU with modified header is received at the UE. The UErecognizes the DRX period is to be adjusted and in step 320 it sends anacknowledgement to the eNB and it adjusts its DRX period at the samesystem frame time considering propagation delay and processing delay asat the eNB.

Referring to FIG. 3 a, in step 342 the eNB receives the ACK and startsthe modified DRX period at the appropriate system frame time. Theprocess then proceeds back to step 332 to see whether the DRX needs tobe adjusted again.

In one embodiment, a DRX command MAC control element could indicate to aUE to transition to a DRX period. In this case, if the eNB wants the UEto transition to a long DRX period due to lack of uplink and downlinktraffic and based on low traffic rates for non real time DRX, undercurrent E-UTRA specifications this requires a change in the DRXconfiguration to be made with an RRC configuration message. A problemwith this is that if the eNB later receives traffic patterns thatrequire a shorter DRX period, the RRC configuration message will need tobe sent again to reconfigure the DRX configuration on the UE.

Instead, a MAC CE could include a “go-to-long-sleep” possibility. Thus,the eNB could provide the UE with an option to go directly to a long DRXperiod without a reconfiguration message explicitly being sent.

Reference is now made to FIG. 10 a. In FIG. 10 a, the process starts atstep 1010 and proceeds to step 1012 in which a check is made todetermine whether a precondition for long DRX exists. As will beappreciated by those skilled in the art, such a precondition couldinclude one or more of: the DRX being configured for non real timetraffic, a lack of uplink and downlink traffic for the UE, low datatransmission to the UE, the position of the UE within a cell and thelikelihood of a transition occurring, among others. If, in step 1012, adetermination is made that the precondition exists the process proceedsto step 1020 in which a long DRX MAC CE is sent to the UE.

Conversely, if the precondition in step 1012 does not exist, the processproceeds to step 1030 in which the short DRX period is maintained andthe process proceeds back to step 1012.

From the UE perspective, reference is now made to FIG. 10 b. The processin FIG. 10 b starts at step 1050 and proceeds to step 1052 in which acheck is made to determine whether short DRX is configured. If not, theprocess proceeds to step 1060 in which long DRX is used.

Conversely, if it is determined in step 1052 that short DRX isconfigured, the process proceeds to step 1070 in which a check is madeto determine whether a long DRX command has been received. As will beappreciated, this long DRX command will be part of a MAC command elementand in one embodiment could be an explicit DRX command indicating longDRX, which is distinct from the previously configured DRX command. Fromstep 1070, if a long DRX command has been received, the process proceedsto step 1072 in which the UE transitions to a long DRX. The process thenproceeds to step 1074 in which a short DRX timer, if configured, isstopped. As will be appreciated, this avoids having a short DRX start onthe expiry of the timer as a long DRX period is signaled.

From step 1074 the process proceeds to step 1080 and ends.

From step 1070, if a long DRX command has not been received the processproceeds to step 1090 in which a short DRX timer is started. The processthen proceeds to step 1092 in which the UE uses a short DRX period. Theuse of the short DRX timer allows the UE to transition to long DRX afterthe timer has expired if no data is received or sent during the timerperiod.

From step 1092 the process proceeds to step 1080 and ends.

The above provides the network with the ability to command the UE to godirectly to long DRX even when short DRX is configured. This savesbattery consumption and network resources when very low traffic isobserved by the eNB. The solution provides a more efficient way totransition to long DRX than by sending RRC level reconfigurationmessages.

As will be appreciated by those skilled in the art, one issue with theabove solutions occurs in the case of a misinterpretation of an ACK or aNACK. Specifically, the hybrid automatic repeat request (HARQ), which isa variation of the ARQ error control method, does not always properlydemodulate an ACK or a NACK due to poor channel conditions. Thus, insome situations, one can be interpreted as the other. By having the DRXactivation and deactivation occur in the MAC-PDU header, an ACK to NACKor NACK to ACK misinterpretation needs to be handled.

A possible solution to the above is the introduction of timer thresholdvalues before activating or deactivating DRX.

When the UE NACKs a MAC-PDU that has DRX header information, the UE isunaware that it should adjust the DRX period. It will expect aretransmission from the eNB. If a NACK to ACK misinterpretation occurs,the eNB receives an ACK and it will not send a retransmission and willchange the DRX period. The UE waits for a time to receive theretransmission. If the UE does not receive the expected retransmission,the waiting time should be limited by an upper threshold (TH-A)considering possible NACK to ACK misinterpretations. If the UE does notreceive a retransmission, it should maintain its current DRX status. TheeNB will expect an exchange of information with the UE at the next DRXperiod. If the UE does not respond, the eNB should revert to theprevious DRX period and attempt to “synchronize” with the UE.

Even when a UE ACKs a MAC-PDU, the UE needs to wait for retransmissiondue to possible ACK to NACK misinterpretation or possible ACK to DTXmisinterpretation by the eNB. The waiting time should be limited by anupper threshold (TH-B).

If the UE is missing data as indicated on the L1/L2 signaling channel,assuming the eNB will retransmit at the next earliest opportunity, theUE needs to check the L1/L2 signaling channel within a certain duration(TH-C). Based on the various threshold parameters above, the minimumtime before DRX activation should therefore be greater than (max(TH-A,TH-B)+TH-C). This threshold value can be signaled either by systembroadcast or RRC signaling.

Various scenarios are considered herein:

DRX activation and ACK to NACK errors:

For an ACK to NACK misinterpretation or an ACK to a discontinuoustransmit (DTX) misinterpretation (i.e. the channel conditions are sopoor that the ACK appears as noise to the receiver), the followingoccurs. The UE receives the DRX activation in the header of the MAC-PDUand sends an ACK to the eNB. The eNB receives the ACK but misinterpretsit as a NACK or a DTX misinterpretation. This results in the UEactivating the DRX before the eNB, which may result in the UE missingthe retransmission of the MAC-PDU from the eNB.

In the situations indicated above, an ACK to NACK or DTXmisinterpretation can be solved by the UE waiting for the timing marginbefore activation of DRX. The margin can be based on the normal timethat it takes a retransmission to occur and weighted by the averagenumber of HARQ retransmissions to the UE that may be experienced. TheDRX activation may be indicated by the RRC signaling or in the MAC-PDUheader extension. When the UE acknowledges the retransmission before thetiming margin expires, the UE will start the DRX at the system frametime considering propagation delay and eNB processing time assuming thattwo consecutive misinterpretations are very unlikely.

DRX Activation and NACK to ACK Errors:

Similarly, if the UE sends a NACK for a MAC-PDU, this could bemisinterpreted as an ACK by the eNB. In the case of DRX activation, theeNB activates the DRX before the UE. If the eNB maintains the CQIresource for the UE for a short period of time after activating DRX, itwill detect that the UE has not activated the DRX indicated by checkingthe frequency of CQI report and it can signal the DRX activation byL1/L2 control signaling. If the eNB releases the CQI resource just afteractivating DRX and assigns it to another UE, CQI reports from the two UEmay collide. The eNB could use Time Division Multiplexing or CodeDivision Multiplexing to avoid the collision.

In the case that the RLC is operating in acknowledged mode (AM), when aNACK to ACK misinterpretation occurs, recovery for DRX synchronizationbetween the eNB and the UE is established via the normal RLCretransmission mechanism. This is because the RLC layer in thetransmitter will determine that the PDU is lost and therefore instigatenormal ARQ recovery by resending the original data not received.

In the case that the RLC is operating in unacknowledged mode (UM mode),no recovery mechanism exists. One solution is, in the HARQ, the receiversends a channel quality indicator (CQI). In continuous reception, thechannel quality indicator is repeated every 100 milliseconds, forexample. Based on the CQI report, the transmitter decides and indicatesa coding rate, modulation scheme, and Transport Block size. Duringactive DRX, the eNB may expect a COI, for example, every second. If theeNB gets this CQI at a different rate (for example 300 milliseconds) itknows that the UE is not in DRX and a correction can occur. For thedeactivation DRX in a NACK to ACK misinterpretation, the UE still thinksit is in DRX while the eNB thinks it is in an active state. This canlead to missed data; however, the next MAC-PDU an indication of DRXdeactivation can again occur.

Thus assuming that the CQI (channel quality indicator) reporting will bealigned to the DRX length, the eNB will know if DRX activation iscompleted in the UE by checking the frequency of CQI reporting. If notcompleted, the eNB may use L1/L2 signaling or send only a MAC-PDU headerto correct the DRX activation or reconfiguration.

Another recovery method can triggered when the eNB receives a TimingAdvance (TA) Request message from a UE that should be in DRX. When theUE returns power to its transceiver and, hence, emerges from the DRXstate, it will often need to send control (e.g. measurement reports) andother data messages the eNB. It is important that the UE have the properTA before sending these messages so that the UE messages do notpartially overlap with messages from other UEs as they arrive at theeNB. Hence, after a DRX cycle the UE will often send a TA Request on arandom access channel so that it can get the proper TA from the eNB. Ifthe TA request arrives at a point when the UE should be in DRX, the eNBwill know that the UE did not receive the last DRX activation ormodification properly. The eNB can then revert to the prior DRX periodfor that UE and recover DRX-period synchronization.

DRX Deactivation and ACK to NACK Errors:

In the case of DRX deactivation or DRX length reconfiguration, an ACK toNACK or DTX misinterpretation leads to the UE deactivating the DRXbefore the eNB, which may require no special handling if the UEacknowledges the normal retransmission from the eNB and the eNBsuccessfully received the ACK.

DRX Deactivation and NACK to ACK Errors:

In the case of DRX deactivation or DRX length reconfiguration, a NACK toACK misinterpretation results in the eNB deactivating the DRX before theUE, which may result in the UE missing the new data transmissions. Thepossible solution to this is that the eNB indicates DRX deactivation ona MAC-PDU header extension of subsequent MAC-PDUs. Assumptions are thatconsecutive misinterpretations are very unlikely and that no DRXreconfiguration is needed when only one MAC-PDU is needed to transmitthe new data which has arrived at the eNB.

DRX Automatic Incrementation

A further consideration is the incremental extension of the DRX. Rulesthat dictate how the DRX period can be incremented or decremented (e.g.by factors of two), in a preferred embodiment, can be signaled duringthe radio bearer (RB) set up. The rules are carried in the RRC RBset-up/reconfiguration or measurement control messages to the UE. Inthis case, if no data is received after N current DRX cycles, the eNBand the UE increase the DRX length to the next larger valueautomatically. This eliminates the need for signaling between the eNBand the UE to increase the DRX length and therefore saves network andbattery resources.

UE Request for DRX

Since the UE terminates all protocols from layer 1 to layer 7, the UEmay be able to determine if it can go into a longest DRX value afterreceiving some specific data packets rather than waiting for the networkto increase the DRX value gradually. In this case, however, it isrequired that the UE have the capability of requesting DRX activation.

As will be appreciated by those in the art, the eNB is not veryintelligent when considering a UE higher layer or application activitiesand thus would normally gradually increase the DRX. However, the UE mayknow that the increase does not need to be gradual in certain cases andcan immediately go to a higher value.

The eNB also signals if the UE may request for DRX activation via theradio resource control radio bearer set-up or a reconfiguration message.However, if the UE needs to inform the eNB of the possibility of a rapidchange, the user plane data is not always available to piggyback arequest for DRX from the UE. In a preferred embodiment, L1/L2 signalingmessages are used. The UE sends a DRX request message to the eNB and theeNB replies with a DRX grant message.

Various considerations may be taken into account by the UE besides theapplication data flow characteristics in determining the proper DRXperiod. The mobility and location within the cell, for example, may betaken into account. If the UE is highly mobile or if it sees goodneighboring cells, the UE may choose to request a shorter DRX period toprepare for a possible handover.

The eNB may also grant a shorter value than requested when it knows thatthe UE is in a high-mobility state or the UE has already missed handoveropportunities, as described below. The eNB can also consider how closethe UE is to the cell's edge. If the UE is close to a cell's edge, theeNB can reject or indicate a shorter time value for the DRX.

If it is allowed by the eNB, the UE indicates a proposed value for a DRXperiod in the optional field of uplink scheduling requests. Even if theUE already has the uplink resources, the message is used without theactual resource request part for the DRX indication.

On the eNB, the eNB responds to the requests by indicating an allowedvalue for the DRX. The activation time is also indicated if the requestfor DRX is granted.

In some embodiments, the DRX request can be integrated in the ULscheduling request and DRX grant can be integrated in the UL schedulinggrant.

The UE also considers its mobility and the likelihood of handover whenrequesting DRX values, which can be based on the channel qualitymeasurement of the serving cell and its neighboring cells. The UE mayalso increase measurement frequencies independently to detect handoverconditions more accurately, as described below. The UE may consider itsmobility status, whether high or low, which may be based on positioningmeasurements, an accelerometer or the filtering of L1 data.

Reference is now made to FIG. 4 a. The process of FIG. 4 starts at step400 and proceeds to step 410 in which the UE receives data.

The process then proceeds to step 412 in which the UE considers the dataand optionally considers other factors as described above. Specifically,the UE may consider the mobility of the UE or the signal strength ofneighboring cells.

Based on the considerations of step 412, the process proceeds to step414 in which it requests a DRX in the L1/L2 uplink scheduling request.

Reference is now made to FIG. 4 b. The process then proceeds to step 416in which the eNB receives the request.

The eNB, in step 418 considers the request and other optional factors asdescribed above. Specifically, the eNB may consider whether the UE hasmissed a cell handover opportunity before or is close to a cellboundary, or is highly mobile. In step 420 the eNB decides whether toallow the request of step 414 based on the factors in step 418. If yes,the process proceeds to step 430 in which it signals that the requesthas been accepted. If no, the process proceeds from step 420 to step 440in which the eNB can either reject the request completely or can suggesta shorter duration for the DRX. Referring to FIG. 4 a, the UE receivesthe response from the eNB in step 442, and may acknowledge in step 444.

As will be appreciated by those skilled in the art, a long DRX may leadto inaccurate handover decisions and executions by the UE. Whenactivating the DRX, the receiver will have less measurement opportunityand thus the accuracy of the channel condition estimation is degraded.Due to the measurement accuracy degradation caused by DRX, the UE maymiss a handover opportunity.

Based on the above, the eNB can reject the request or grant a shortenedDRX value if it knows that the UE is located close to a cell edge. Thisdecision can be based on the current timing adjustment value assumingits available, the UE mobility status, whether high or low, the numberof handovers within a certain period considering cell radius or thenumber of occasions that the UE goes out of the serving cell or indeedknowledge regarding the actual size of the cell (e.g. macro, micro orpico). These are all factors that can be considered in step 418 of FIG.4 b.

Measurement Accuracy

A third factor for DRX in the LTE-ACTIVE state is the possibility ofmissed handover opportunities. Since the UE receiver is turned offduring the DRX period, the measurement quality of serving andneighboring cells is likely degraded compared to a continuousmeasurement. This degradation may lead to premature handover or missedhandover opportunities, which should be avoided to the maximum extentpossible.

In order to reduce the number of premature handovers or missed handoveropportunities in DRX, in a preferred embodiment the UE is allowed tohave a shorter measurement cycle than the DRX cycle when necessary. Forexample, if the channel quality of the serving cell is lower than athreshold value A, the UE may start continuous measurements or shortermeasurement cycles to prepare for a possible handover condition. If itturns out to be a false alarm, i.e. if the channel quality obtained bythe continuous measurement is greater than a threshold value B, the UEcan go back to the measurement cycle equal to the DRX cycle. As will beappreciated by those skilled in the art, the two threshold valuesrepresent better channel conditions than a value that triggers handoverso that a sufficient level of accuracy is obtained when required toevaluate handover conditions, thus missed handover opportunities can bereduced.

In one embodiment of the present disclosure, the measurement intervalmay be configured to be equal to a DRX interval divided by N where N isan integer. This would be in the situation where the mobile may beexpecting a handover and/or there is high mobility.

The network can configure the thresholds and the shorter measurementcycles, and this can be signaled to the UE via broadcast information oran RRC measurement control message. The MAC-PDU header can indicate tothe network the shortened DRX cycle value once the UE has shortened themeasurement cycle.

An example of the above is when there is an RRC connection or a radiobearer is established. In this case, the eNB can indicate the twochannel quality values to which shorter DRX is started and stoppedrespectively, and the ratio between measurement and DRX cycles.

On the UE, the UE acts on the RRC signaling and starts or stops theshorter measurement cycles according to the measurement of channelquality compared to the threshold values.

Reference is made to FIG. 5. FIG. 5 illustrates various zones where theUE may be situated including threshold values to indicate the DRX cycle.In the first zone 510, the DRX cycle equals the measurement cycle. TheUE stays within this zone until it reaches a threshold 520 in which itneeds to start a shorter measurement cycle.

The UE stays with the shorter measurement cycle until either the signaldegrades to indicate a handover condition 530 or if the signal improvesuntil it achieves an upper threshold 540, at which point the DRX cydeand measurement cyde equal each other.

Preferably the eNB signals the following information in the radio bearerset-up or in a measurement control message:

-   -   A higher threshold value used to lengthen the DRX cycle. This        higher threshold value indicates higher channel quality and/or        signal strength;    -   A lower threshold value used to shorten the DRX cycle. The lower        threshold value indicates lower channel quality and/or signal        strength;    -   Time-to-trigger associated with the higher threshold value and        the lower threshold value; and    -   The handover condition, such as the “best cell changed” and the        measurement cycle equals zero, indicating continuous        measurement.

The diagram of FIG. 7 shows an example in which the channel quality orsignal power (as indicated in measurement reports) goes below the lowerthreshold value (LTV) and then goes above the higher threshold value(HTV) without uplink data. In this case, the shortened measurementperiod is implemented between A and B, whereas the DRX cyde equals themeasurement cycle before A and after B.

FIG. 8 shows an example in which the channel quality or signal power (asindicated in measurement reports) goes below the lower threshold value(LTV) and then goes above the higher threshold value (HTV) with uplink(UL) data. In this case, the UE goes to a short measurement cycle if thechannel quality is below the lower threshold value more than a certainduration (time to trigger). If there is uplink data, the UE starts aninitial UL access procedure to obtain a UL resource grant by sending thescheduling request. The scheduling request or the header of the uplinkMAC-PDU could indicate a request for a shorter DRX period. The eNBresponds to the request by sending scheduling grant message with apreferred DRX value or the eNB could indicate a preferred DRX value inthe next downlink MAC-PDU. When the scheduling grant is received or thedownlink MAC-PDU is acknowledged, the eNB can start using the new DRXvalue. The figure then shows the channel quality or signal power (asindicated in measurement reports) goes above a higher threshold valuefor a certain duration (time to trigger). The UE indicates a request fora longer DRX value in the scheduling request or in the header of theMAC-PDU if UL data is available. The eNB responds to the request bysending a scheduling grant message with a preferred DRX value and anindication to start the automatic mode or the eNB could indicate apreferred DRX value with an indication to start the automatic mode inthe header of the next downlink MAC-PDU. When the scheduling grant isreceived or the downlink MAC-PDU is acknowledged, automatic mode isstarted with the initial DRX value specified by the eNB. If no data isavailable then the UE needs to send a L1/L2 control message to requestthe automatic increment of DRX.

The example of FIG. 9 shows a handover condition trigger. In this case,the signal is gradually degrading until it proceeds below a lowerthreshold value for a certain time to trigger, at which point, the UEstarts using a shorter measurement. The UE then sees the handovercondition for a certain duration (time to trigger). At this moment theUE initiates the UL access procedure and transmits a scheduling requestin order to obtain UL resources for the measurement report message. DRXvalue of zero or a request for going back to continuous reception modecan be indicated in the scheduling request or in the MAC-PDU carryingthe measurement report message. The eNB responds to the request bysending scheduling grant message with the preferred DRX value of zero orthe eNB could indicate a preferred DRX value of zero in the nextdownlink MAC-PDU. When the scheduling grant is received or the downlinkMAC-PDU is acknowledged, both sides deactivate DRX. On handover, the UEreceives a handover command and obtains downlink synchronization to thetarget cell. The UE then indicates the channel quality and/or signalstrength of the target cell in the handover complete response. The eNBcan then evaluate when it is safe to activate DRX. If so the eNBindicates DRX activation in the downlink (DL) MAC-PDU header or L1/L2control signaling.

In the above paragraphs, the requests made by the UE for a shorter orlonger DRX period or the DRX value itself are in the scheduling requestor the header of the uplink MAC header. The eNB responds to the UE, byspecifying the preferred DRX period with an indication if an automaticDRX increase/decrease rule can be applied, within the scheduling grantor downlink MAC-PDU header.

In another embodiment, the scheduling request indicates the cause ofuplink access. For example, suppose that during a DRX period of 2.56seconds a VOIP call is originated. In order for the network to respondthe VOIP call setup promptly, the UE sends the scheduling request with acause of uplink access, e.g. call setup. The eNB replies to the requestby sending a scheduling grant indicating a DRX value of zero (thepreferred DRX value).

Detection and Handling of Very Late Handover

In order to utilize the DRX in the LTE_ACTIVE state, a standardizedcriterion for the UE to determine if a handover opportunity is missed ispreferable. If such a condition is satisfied, the UE should establish aconnection to a neighboring cell rather than the serving cell. As willbe appreciated by those skilled in the art, in the LTE infrastructure,only network based handover procedures apply and there are no UE basedprocedures such as cell reselection as used in UMTS.

If, in a preferred embodiment, the channel quality of the serving cellis less than a neighboring cell by a threshold value C for a certaintime duration T, the UE is required to connect itself to the neighboringcell on the target eNB. The value C and T can be signaled by systembroadcast information or RRC signaling.

The process for switching to the target eNB includes the steps of:

-   -   1. Start UL initial access procedure to obtain a timing advance        value for the target cell and uplink resources for the        subsequent control messages;    -   2. Transmit a reconnect request to the target eNB with the        current RNTI (radio network temporary identifier) and previous        cell ID;    -   3. The target eNB contacts the serving eNB in order to obtain        the UE context and downlink data needs to be transferred. The        target eNB also connects itself to the access gateway and        removes the serving eNB from the aGW; and    -   4. The target eNB transmits a reconnect response to the UE with        a new RNTI and uplink grant.

An optional component includes a status message to be carried over thereconnect request and response so that the amount of data transferredbetween the target and serving eNB and between the target and servingeNB and the air interface with the UE can be minimized.

Optimizations include the reconnect request in step 2 above to be sentwith a status report showing the PDCP (packet data convergence protocol)SDU (service data unit) sequence numbers which the UE has receivedsuccessfully. This information helps to reduce the amount of downlinkuser data to be transferred from the serving to the target eNB and overthe air to the UE. Since the RLC is likely reset in the procedure, PDCPSDU sequence numbers need to be used.

Likewise, the reconnect response can be sent with a status reportshowing PDCP SDU sequence numbers which the serving eNB receivessuccessfully so that the UE can retransmit data that was missed.

Further, if the target eNB finds that there is no data to be transferredfrom the serving eNB and from the aGW, the reconnect response indicatesDRX activation.

The above is illustrated in FIG. 6 a in which, in step 612, the UEobtains a timing advance value for the target cell and uplink resourcesfor the subsequent control messages. The process then proceeds to step614 in which the UE transmits a reconnect request to the target eNB withthe current RNTI and cell ID. The UE then waits for and acknowledges aresponse from the target eNB in step 650.

Referring to FIG. 6 b, the target eNB receives the request at step 615and then proceeds to step 616 in which the target eNB contacts theserving eNB in order to obtain the UE context.

In step 618, the target eNB transmits a reconnect response to the UEwith the new RNTI and uplink grant.

The above can be implemented on any UE. Such UEs include, but are notlimited to, personal digital assistants, cellular telephones, wirelessdata devices, among others.

The embodiments described herein are examples of structures, systems ormethods having elements corresponding to elements of the techniques ofthis application. This written description may enable those skilled inthe art to make and use embodiments having alternative elements thatlikewise correspond to the elements of the techniques of thisapplication. The intended scope of the techniques of this applicationthus includes other structures, systems or methods that do not differfrom the techniques of this application as described herein, and furtherincludes other structures, systems or methods with insubstantialdifferences from the techniques of this application as described herein.

1. A method for configuring a discontinuous reception ‘DRX’ period at auser equipment comprising: determining whether a short DRX period isconfigured at the user equipment; if no, setting a long DRX period; ifyes, determining whether a long DRX command was received in a mediumaccess control ‘MAC’ control element; if yes, setting the long DRXperiod; if no, starting a short DRX timer and setting a short DRXperiod.
 2. The method of claim 1, wherein the user equipment maintains ashort DRX configuration.
 3. The method of claim 1, wherein the DRX isconfigured for non real time traffic.
 4. The method of claim 1, furthercomprising the step of stopping a short DRX timer if the long DRXcommand in the medium access control ‘MAC’ control element was received.5. A user equipment adapted to configure a discontinuous reception ‘DRX’period, comprising: a communications subsystem, said radio subsystemadapted to receive a medium access control ‘MAC’ control element; amemory, said memory adapted to store information for the medium accesscontrol element; and a processor, said processor adapted to: determinewhether a short DRX period is configured at the user equipment; if no,set a long DRX period; if yes, determine whether a long DRX command wasreceived in the medium access control ‘MAC’ control element; if yes, setthe long DRX period; if no, start a short DRX timer and set a short DRXperiod.
 6. The user equipment of claim 5, wherein the memory is adaptedto maintain a short DRX configuration.
 7. The user equipment of claim 5,wherein the DRX is configured for non real time traffic.
 8. The userequipment of claim 1, wherein the processor is further adapted to stop ashort DRX timer if the long DRX command in the medium access control‘MAC’ control element was received.
 9. A method for configuring adiscontinuous reception ‘DRX’ period from an evolved Node B ‘eNB’comprising: determining whether a precondition has been met to have auser equipment transition directly to a long DRX period, if yes, sendinga MAC control element for a long DRX period, if no, maintaining a shortDRX period.
 10. The method of claim 9, wherein the precondition is atleast one of the group consisting of: DRX being configured for non realtime traffic; traffic volume being low; no uplink and downlinktransmission exists; and no transition for a user equipment is expected.11. The method of claim 9, wherein the maintaining step utilizes apreconfigured DRX configuration on the user equipment.
 12. An evolvedNode B adapted to configure a discontinuous reception ‘DRX’ comprising:a communications system; a memory; and a processor, the processoradapted to determine whether a precondition has been met to have a userequipment transition directly to a long DRX period, if yes, theprocessor adapted to send, through the communications subsystem, amedium access control ‘MAC’ control element for a long DRX period; ifno, the processor adapted to maintain a short DRX period.
 13. Theevolved Node B of claim 12, wherein the precondition is at least one ofthe group consisting of: DRX being configured for non real time traffic;traffic volume being low; no uplink and downlink transmission exists;and no transition for a user equipment is expected.